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1/15 n two n-channel mosfets control and dual independent current supervision for over current protection n dual supply operation n from +3/-5v operating voltage n step-up converter : vcc +13.5v output voltage n adjustable protection mode (ctrip 1/2) n shutdown output status n few external components description the TD230 is designed to control two n-channel mosfets used as power switches in circuit breaking applications. its current supervision and immediate action on the switches ensure high security for the boards and the supplies thus protected agains short-cir- cuit or over current. in case of short-circuit or over current detection, the TD230 immediately switches off the corre- sponding mosfet, thus disconnecting the board from the supply. after several automatic restart at- tempts, a definitive shutdown of the circuit is done if the shortcuircuit or over current persists over an externally adjustable time, until the TD230 is reset by temporary inhibit signal or temporary switch- ing off of the power supply (hot disconnection/re- connection). if the board is disconnected from the positive sup- ply by the TD230 it will automatically be disjoncted from the negative supply too. TD230 integrates an induction step-up converter that provides 13.5v above the positive rail to drive the high side mosfet. order code n = dual in line package (dip) d = small outline package (so pin connections (top view) part number temperature range package nd TD230i -40c, +125c n dip16 (plastic package) d so16 (plastic micropackage) 1 2 3 4 5 6 7 9 10 11 12 13 14 8 15 16 pvcc lboost cboost pm1 gnd pm2 oscgnd nvcc ref1 gc1 sensp inhibit shutdown sensn gc2 ref2 electronic circuit breaker december 2001 TD230
TD230 2/15 block diagram absolute maximum ratings operating conditions instruction for use osc step-up pvcc vsp1 osc gnd ip2 vsp2 ip3 in3 in2 vsn2 pvcc pvcc lboost cboost ref1 ip1 sw1 sensp sensn sw2 pvcc in1 gc2 ref2 vsn1 nvcc vsp3 vsn3 inhibit pm1 shutdown gnd pm2 gc1 symbol parameter value unit v cc + positive supply voltage +22 v v cc - negative supply voltage -22 v inhibit input voltage 7 v shutdown input voltage 7 v pm1/pm2 input voltage 7 v t j operating junction temperature -40 to +150 c t amb operating ambient temperature -40 to +125 c t stg storage temperature range -65 to +150 c symbol parameter value unit v cc supply voltage 18 v symbol parameter value unit c bypass bypass capacitor (each supply) 1 f
TD230 3/15 electrical characteristics v cc = 5v, t amb = 25c, l boost = 220h, c boost = 100nf (unless otherwise specified) symbol parameter min. typ. max. unit supply v cc + positive supply voltage 2.7 18 v v cc - negative supply voltage -18 -4.5 v i cc + positive supply current charge pump inactivated charge pump activated l boost = 220h, c boost = 100nf 1.8 2.3 3 4 ma i cc - negative supply current charge pump activated/inactivated -0.7 -1.5 ma logic input (inhibit) v ih high input voltage 2 6 v v il low input voltage 0 0.8 v tp propagation delay gc1/2 (without load) 0.5 2 s logic output (shutdown-open drain) v ol low output voltage (2ma) 0.8 v i oh high output current (6v) 1 na t s shutdown response time (sens p/n shutdown whthout load) 8 15 s step-up converter v boost step-up output voltage v cc + +10 v cc + +13.4 v cc + +15 v t vboost rise time for v boost (10 to 90%) 250 800 s v rip output ripple voltage 0.15 0.5 v input comparators v i threshold (pv cc - ref1, nv cc - ref2) 56 63 71 mv t re response time (gc1/2 - without load) 2 3 s t i inhibition time (without load) 300 ns voltage sources vsp2 vsn2 threshold sense pos/neg 0.7 v cc 0.75 v cc 0.8 v cc v vsp3 vsn3 threshold protection mode 1.10 1.20 1.30 v current sources ip1, in1 soft start current sources 10 15 20 a ip2, in2 protection mode current sources (loading c trip 1/2 ) 345a ip3, in3 protection mode current sources (discharging c trip 1/2 ) 0.6 1 1.4 a switches r on on-resistance of the switches - sw1/sw2 90 200 w
TD230 4/15 figure 1 : dual electronic circuit breaker application figure 2 : single electronic circuit breaker application 1 2 3 4 5 6 7 9 10 11 12 13 14 8 15 16 pvcc lboost cboost pm1 gnd pm2 oscgnd nvcc ref1 gc1 sensp inhibit shutdown sensn gc2 ref2 vcc+ gnd vcc- lboost ctrip1 ctrip2 rs2 nmos to board css1 control nmos from board css2 rs1 cboost 1 2 3 4 5 6 7 8 vcc+ gnd lboost ctrip1 cboost 9 10 11 12 13 14 15 16 control pvcc lboost cboost pm1 gnd pm2 oscgnd nvcc ref1 gc1 sensp inhibit shutdown sensn gc2 ref2 rs1 nmos to board css1
TD230 5/15 timing diagrams pvcc-vref (=vrs) vi sensp pvcc- e gc1-sensp = vgs 13.4v ~5v pm1=vctrip1 pvcc vsp3 shutdown inhibit hiz ttl normal function status short circuit current limitation normal function normal current normal current short circuit current limitation circuit off power off on normal current normal function inhibit hi lo normal current normal function off tpm1 # (ctrip1.vsp3) ip2-ip3 ts tp tss # pvcc.css ip1 normal function events short circuit current limitation normal function normal current normal current pvcc-vref (=vrs) vi gc1-sensp = vgs 13.4v ~5v pvcc-vref (=vrs) vi gc1-sensp = vgs 13.4v ~5v t < ti ti tre toff # ron.css
6/15 introduction over current and short circuit protection is a con- stant concern for todays engineers. more and more applications in different segments (telecom, automotive, industrial, computer...) require al- ways improved reliability after delivery : mainte- nance costs are an ever more worrying source of expenses and customers dissatisfaction. alternatives for short circuit or over current protec- tions are the fuses and the ptc (positive temper- ature coefficient) resistors. the first are a cheap but destructive solution ; the second are tied to a time constant due to self heating which is often in- compatible with the host equipments require- ments. in both cases, a coil can be added for an efficient limitation of current surges, to the detriment of weight and volume. none of these solutions is fully satisfactory for a reliable, immediate and non destructible short cir- cuit and over current protection. 1. electronic circuit breaker the electronic circuit breaker TD230 is the conve- nient solution for any industrial who wants at the same time : q immediate, efficient and resettable protec- tion for his equipment q versatility regarding different applications q easy and quick design-in q low component count q low cost the electronic circuit breaker TD230 is to be used with a minimal amount of external and low cost components to drive one or two n-channel mos- fets (in respectively single or dual supply appli- cations) used as power switches between the dc power supplies and the equipments to be protected. the TD230 immediately reacts (3 m s max. without load) whenever an over current is detected by switching off the corresponding mosfet. several automatic restart attempts are made unless the fault persists over an externally adjustable amount of time after which the power mosfet is defini- tively switched off, waiting for a reset. if the fault is detected on the positive supply, the definitive shutdown will also disconnect the nega- tive power supply and set a warning low level on the shutdown pin. if the fault is detected on the negative supply, the definitive shutdown will dis- connect only the negative power supply, and let the positive part of the circuit undisturbed. the whole system can be reset in three ways : q by switching off the power supplies q by unplugging and re-plugging the card (live insertion) q by setting the inhibit pin active during a short time (allowing remote reset) 2. how to use the TD230 ? the typical configuration of the TD230 - electronic circuit breaker - in a dual supply topology is shown in figure 1 . in this configuration, both nmos 1/2 are used as power switches which connect the equipments to the power supplies, thus ensuring low voltage drop through the on-resistances (rdson) of nmos 1/2 . 2.1. current limitation when an over current condition (i oc ) is detected through the low ohmic shunt resistors r s 1/2 as giv- en under equation (i) : q v rs 1/2 = i oc x r s > 63mv typ. (i) the gate of the corresponding mosfet 1/2 is dis- charged immediately, thus disconnecting the board/equipment from the power supply. note that the over current condition is given by the constant product i oc x r s = 63mv, which means that the ioc limit is directly given by the choice of the shunt resistors r s1/2 values. the TD230 automatically makes restart attempts by slowly recharging the gate of the mosfet 1/2 with a 15 m a typ. current source ensuring thus slow ramp with the typical time constant before recon- duction shown in equation (ii) : q t on = ciss x vth / 15 m a (ii) where ciss is the input capacitance of the power mosfet 1/2 and vth, the threshold voltage of the mosfet (typically 5v). this reconduction time can be extended with an external soft start capacitor c ss1/2 as shown in application note electronic circuit breaker by r. liou
TD230 7/15 figure 1 c iss will therefore simply be replaced by c iss + c ss 1/2 . figure 1 : dual electronic circuit breaker application if the fault (over current condition) still remains af- ter the reconduction state of the mosfet 1/2 has been reached, the current through nmos 1/2 will overpass the limitation given by equation (i), and the nmos 1/2 will immediately be switched off again. figure 2 shows the current limitation which is op- erated on every restart attempt. figure 2 : TD230 as current limitor trace a represents the gate-source voltage of the power mosfet (0 to 13,4v). trace b represents the voltage across the sense resistor (68m w ) in direct relation with the current through it (0 to ~1a). note that the first current peak which is due to an over current is limited only by the reaction time of the TD230 . this off time is tied to the value of the external soft start capacitor c ss 1/2 by equation (iii) : q t off = r dson x c ss (iii) while in current limitation mode, the nmos 1/2 dis- sipates low power due to the fact that the on/off cycle time rate is very low. note that the higher the value of c ss1/2 are, the more the nmos 1/2 will stay in linear mode during current limitation. note that at power on, or in the case of live inser- tion, the inrush current is automatically limited thanks to the slow gate charge of the mosfet which switches on softly due to the time constant given in equation (ii). 2.2. fault time limitation the repetitive switching off of the mosfet will come to an end under two conditions : q either the fault has disappeared, and the current through the shunt resistors r s 1/2 has come back to its nominal value : the system keeps running normally. external line defaults (lightning, line breakage, etc...) are usual causes for such temporary over currents. q either the repetitive switching off has lasted over an externally adjustable time and the TD230 has definitively switched off the cor- responding nmos : the system waits to be reset. equipment faults (component short circuit, over heat, etc ...) are usual causes for lasting over cur- rents. this fault time supervision is done by the compar- ison of the output voltage to 75% of the nominal supply voltage. as soon as the output voltage is detected under 0.75xvcc(+/-), the corresponding external capacitors c trip1/2 is charged by a fixed current source i p/n2 - i p/n3 (3 m a). when the voltage across c trip1/2 reaches 1.20v, the corresponding nmos is definitively switched off and the shut- down pin is active low. to avoid cumulative charging of the protection ca- pacitors c trip 1/2 in case of successive overcurrent 1 2 3 4 5 6 7 9 10 11 12 13 14 8 15 16 pvcc lboost cboost pm1 gnd pm2 oscgnd nvcc ref1 gc1 sensp inhibit shutdown sensn gc2 ref2 vcc+ gnd vcc- lboost ctrip1 ctrip2 rs2 nmos to board css1 control nmos from board css2 rs1 cboost
TD230 8/15 conditions, the capacitors c trip 1/2 are constantly discharged by another fixed current source ip/n3 which value is a fourth of i p/n2 (1 m a). figure 3 : fault time limitation trace 1 represents the c boost voltage (0 to 5+13,4 = 18,4v) trace 2 represents the c trip1 voltage. the value of the capacitors c trip 1/2 should be cho- sen in relation with the required protection time as indicated in equation (iv) : q c trip1/2 = (i p/n2 - i p/n3 ) x t protect1/2 / vs pn/3 (iv) where t protect 1/2 is the time defined by the user be- fore a definitive resettable shutdown of mos- fet 1/2 . equation (iv) can be translated to : q c trip 1/2 = t protect 1/2 x 3 m a / 1.20v (iv) note that the positive power supply disjonction leads to the negative power supply disjonction, whereas the opposite is not true. 2.3. step-up converter to ensure proper voltage on the gate of the posi- tive supply nmos1 (v gs = 13.4v typ), the TD230 integrates a step-up converter which is to be boosted with two small low cost external compo- nents : an inductor l boost and a capacitor c boost , as shown in figure 4 . figure 4 : step up converter external components the principle of this inductive step-up converter is to pump charges in the tank capacitor c boost fol- lowing the equation (v) : figure 5 : internal step up schematic q v(c boost ) = v cc+ + 13.4v typ (v) charges are pumped by means of an oscillator commanded switch, and stored in the c boost tank capacitor through a diode as shown on figure 5 . when the voltage across c boost reaches v cc + +13.4v typ, the oscillator is stopped. this cre- ates a ripple voltage with an amplitude of 0.2v. note that the min and max values of v(c boost ) comprised between v cc + +10v and v cc + +15v al- ready take the ripple voltage into account. rsense mos lboost c boost sense step up driver TD230 lboost cboos t TD230 osc regulation
TD230 9/15 proper operation of this step-up converter is guar- anteed at as low as 2.7v with a rise time (0 to 90% of v(c boost )) in the range of 700 m s at 2.7v which is the worst case. at 5v, the rise time of v(c boost ) is 250 m s typ. the c boost voltage wave form at power on under 5v supply voltage is shown on figure 6 . figure 6 : step up converter rise time trace 1 represents the power supply voltage (0 to 5v). trace 2 represents the c boost voltage at power on (0 to 5+13,4 = 18,4v). table (a) summerizes the recommended values of the c boost and l boost to ensure optimized gate charge and low ripple voltage with their corre- sponding maximum current surge (i pk ) and nomi- nal consumption (i cc ) of the TD230 for the most common power supply values. for each power supply value is also given the recommended value of a bypass capacitor (c by ) on the power sup- plies. note that both c boost and l boost are available in surface mount packages. table (a) : recommended values for c boost and l boost 2.4. single supply breaker application the TD230 is perfectly suited to fit in single sup- plied applications (ex 0-5v), and can drive only one power mosfet used as high side power switch. figure 7 shows how TD230 can be used as a sin- gle circuit breaker with the same performances. figure 7 : single electronic circuit breaker application in this case, the external components consist in one boost inductor, one sense resistor, three ca- pacitors, and one power mosfet. 2.5. typical telecom line cards protection application one of the typical applications where the TD230 can display all its technical advantages is in an ex- change telecom cards protection. sometimes fif- ty cards or more are to be supplied with the same power supply (+/-5v, 1kw), and a decentralized protection is needed because one card may be faulty, but should not penalize the others with un- adapted protection system. the risk of complete breakdown of the system must be eradicated. in this application the two above described over current causes (external line perturbation or inter- nal component fault) are likely to happen. in the first case, the current limitation on each card will ensure undammaging on-board conditions, and in the second case, the faulty card will be disjoncted from the power supply until reset. figure 8 shows a typical telecom application with decentralized protection. in this application, the positive power supply serves the logic control and analog signals where- as the negative power supply is dedicated to the analog. v cc + v c boost nf l boost m h i pk ma v rip mv i cc ma c by m f 2.7 47 100 68 60 190 100 5>1 5 100 220 35 120 2.5 1 10 100 220 470 33 220 100 2.2 1 12 220 470 39 150 2.2 1 14 220 680 34 150 2.4 1 18 220 1000 31 200 2.7 1 1 2 3 4 5 6 7 8 vcc+ gnd lboost ctrip1 cboost 9 10 11 12 13 14 15 16 control pvcc lboost cboost pm1 gnd pm2 oscgnd nvcc ref1 gc1 sensp inhibit shutdown sensn gc2 ref2 rs1 nmos to board css1
TD230 10/15 figure 8 : decentralized protection therefore, when a fault appears on the positive rail, the definitive shutdown of the positive nmos will lead to the shutdown of the negative nmos, but when a fault appears on the negative rail, the definitive shutdown of the negative nmos will have no effect on the positive nmos. several possibilities are offered to reset the whole system when it has been led to definitive shut- down : q the card can be unplugged and plugged back (live insertion) q the inhibit pin can be set to active state during a short time (100 m s typ or more) in the case of remote control facilities 3. performances and evaluation all the curves shown in this application note have been realized with the TD230 evaluation board. the external conditions and components were as listed hereafter : q v cc + = 5v q v cc - = -5v q suppliable output short circuit current = 5a q ic = TD230 q mosfet 1 = buz71 q mosfet 2 = buz71 q l boost = 220 m h q c boost = 100nf q c trip1 = 10 m f q c trip2 = 10 m f q r s1 = 68m w q r s2 = 68m w q c ss1 = 1nf q c ss2 = 1nf q positive bypass = 4.7 m f (plastic) q negative bypass = 4.7 m f (plastic) the evaluation board is available and allows to test the performances of the TD230 . the layout and schematic of this evaluation board are given on figures 9a-9b-9c . 4. cautions for proper use of the TD230 as a reliable protec- tion device, a few precautions must be taken : 1. proper bypass capacitors must be connected as close as possible to the power pins of the TD230 (pv cc , nv cc , gnd). some recommended values are given in table (a). 2. the oscgnd pin must be tied to the gnd pin externally (printed board) to ensure proper step-up converter reference. if not, the step-up converter will not start. 3. the inhibit pin is a cmos/ttl compatible in- put which should therefore not be left unconnect- ed. the absolute maximum rating of this input is 7v. it should be tied to the ttl compatible output of an eventual control block, or, if it should not be used, tied to the gnd pin. TD230 TD230 TD230 TD230 board1 board2 board3 boardn vcc+ power supply gnd vcc-
TD230 11/15 figure 9a: pcb (not to scale) figure 9c: schematic figure 9b : silkscreen 4. the shutdown pin is an open drain cmos/ ttl compatible output which should be tied to the ttl compatible input of an eventual control block. the absolute maximum rating of this output is 7v. in the case of a visual alarm, a led is likely to be tied to the positive power supply which can be de- structive for the shutdown output if the power sup- ply is over 7v. an easy way to eliminate this is to add a 6v zener diode between the shutdown out- put and the ground as shown on figure 10 . 5. the time constant of the protection mode (given by the charge of ctrip 1/2 capacitors) must be greater than the time constant of the restart at- tempts (given by the charge of the c ss 1/2 soft start capacitors). this condition can be described as follows : q v sp1/2 x c trip1/2 / i p/n2 > v th1/2 x (c ss1/2 +c iss1/2 ) / i p/n1
TD230 12/15 figure 10 : visual alarm-shutdown where c iss1/2 , c ss1/2 , v th1/2 , i p/n1 are respectively the input capacitance, the soft start capacitor, the threshold voltage and the internal gate current sources of nmos 1/2 ; and where v sp1/2 , c trip1/2 , i p/ n2 are respectively the voltage source, current source and external capacitor of the protection mode pins pm 1/2 . considering the typical values of v sp1/2 , i p/n2 , i p/n1 , and the fact that classical power mosfets have a threshold voltage around 5v, this condition can be translated to inequation (vi) : q c trip1/2 > 0.8 x (c ss1/2 + c iss ) (vi) if c iss = 1nf and c ss1/2 = 4.7nf, c trip1/2 should be superior to 4.56nf. table (b) summerizes protection mode time constants corresponding to different c trip1/2 val- ues. table (b) : protection mode time constants 5. enhancements the performances of TD230 are well adapted to most of the circuit breaking applications in many differents industry segments (telecom, automo- tive, industrial, computer etc...), but in the case of very demanding environment, or outstanding fea- tures, the few following advices may be helpful. 5.1. step-up noise reduction the inductive step-up converter inevitably gener- ates current peaks in the output of the power switch which, in most cases are, are not worrying. but in some very demanding applications, it is necessary to remove this noise. a good way to eliminate such peaks is to add a re- sistor connected in series with the inductance and an electrolytic capacitor between the common point of resistor and inductance, and ground of the step-up converter as shown on figure 11 . figure 11 : step up noise reduction the resistors voltage drop will be due to the prod- uct of the average consumption current with the resistors value and the inductive current peaks will be totally absorbed by the capacitor. with a 100 w resistor, the voltage drop is negligible and the attenuation good with a 4.7 m f as shown on figure 12 . figure 12 : step up noise reductio c trip1/2 time constant range for protection mode - shutdown - 22nf #10ms 220nf #100ms 2.2 m f#1s 22 m f #10s TD230 shutdown vcc+ rsense lboost cboost TD230 c r
TD230 13/15 trace a represents the ripple voltage on c boost (200mv width). trace b represents the voltage perturbation due to the step-up converter on the output (source of the power mosfet = board power supply). traces 1 and 2 represent the same, but improved thanks to the step-up noise reduction rc. 5.2. precision enhancement if the system needs accurate current limitation in an environment subject to very wide temperature- variations, a good way to compensate fluctuations due to temperature variations is to use a ctn as described in figure 13 . figure 13 : wide temperature variations 5.3. temporisation in some cases, it can be useful to let short current peaks pass without reaction of the breaker, though these are of higher value than the fixed current limit. this enables the electronic circuit breaker to be- have as a thermal disjonctor. this behaviour can easily be given by adding an rc constant as shown on figure 14. figure 14 : temporisation rsense TD230 ctn r r rsense TD230 c r
TD230 14/15 package mechanical data 16 pins - plastic dip dimensions millimeters inches min. typ. max. min. typ. max. a1 0.51 0.020 b 0.77 1.65 0.030 0.065 b 0.5 0.020 b1 0.25 0.010 d 20 0.787 e 8.5 0.335 e 2.54 0.100 e3 17.78 0.700 f 7.1 0.280 i 5.1 0.201 l 3.3 0.130 z 1.27 0.050
TD230 15/15 package mechanical data 16 pins - plastic micropackage (so) dimensions millimeters inches min. typ. max. min. typ. max. a 1.75 0.069 a1 0.1 0.2 0.004 0.008 a2 1.6 0.063 b 0.35 0.46 0.014 0.018 b1 0.19 0.25 0.007 0.010 c 0.5 0.020 c1 45 (typ.) d 9.8 10 0.386 0.394 e 5.8 6.2 0.228 0.244 e 1.27 0.050 e3 8.89 0.350 f 3.8 4.0 0.150 0.157 g 4.6 5.3 0.181 0.209 l 0.5 1.27 0.020 0.050 m 0.62 0.024 s 8 (max.) information furnished is believed to be accurate and reliable. however, stmicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result f rom its use. no license is granted by implication or otherwise under any patent or patent rights of stmicroelectronics. specificati ons mentioned in this publication are subject to change without notice. this publication supersedes and replaces all information previously supplied. stmicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of stmicroelectronics. ? the st logo is a registered trademark of stmicroelectronics ? 2000 stmicroelectronics - printed in italy - all rights reserved stmicroelectronics group of companies australia - brazil - china - finland - france - germany - hong kong - india - italy - japan - malaysia - malta - morocco singapore - spain - sweden - switzerland - united kingdom ? http://www.st.com

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